Circuits for a voltage-sensitive switch



R. F. SHOEMAKER El'AL 2,909,122

CIRCUITS FOR A VOLTAGE-SENSITIVE SWITCH Filed March 15, 1957 Oct. 20,1959 I2 I8 l l l ll LOW- IMPEDANCE l3 [jifgLsE SOURCE /[3 LOW- IMPEDANCEDETONATOR l4 VOLTAGE SENSITIVE SWITCH L0 I-"t H I: .21-

VOLTAGE SENSITIVE 20 -10 MEGOHMS SWITCH LOW-IMPEDANCE 23 DETONATOR PULSEI; 4 SOURCE 25 lo MEGOHMS fig. .5-

VOLTAGE SENSITIVE SWIT INVENTORJ;

3| BY Robe/"Z M Talc/{er Henry f. Haw/mus 245. 5% y-noll ffffiga. w

E 730k en? E 5/7 oemakef United States Patent 1 O CIRCUITS FOR AVOLTAGE-SENSITIVE SWITCH Robert F. Shoemaker, McLean, Va., Robert W.Tucker, Rockville, Md., and Henry P. Kalmus, Washington, D.C., assignorsto the United States of'America as represented 'by the Secretary of theArmy ApplicationMalch 15, 1957, Serial No. 646,507

1 Claim. (Cl. 102-702) (Granted under Title 35, U.S. Code (1952), sec.266) The invention describedhereinmay be manufactured and used. by orfor the Government for governmental purposes without the payment to usof any royalty thereon.

This invention relates to means toractuating detonators in ordnancefuzes, and in particular to acircuit including a single shot voltageresponsive capacitive switch.

It is an object of this invention to provide a circuit for theactivating of a detonator and with this circuit includinga single shotvoltage responsive switch to displace the thyratron customarily employedin detonator activating circuits. M

It is an object of this invention to provide a detonator activatingcircuit in which the customary thyratron is displaced by a single shotvoltage responsive switch of very small dimensions, of ruggedconstruction, sealed against atmospheric conditions, and capable ofbeing made at a cost which is very low in comparison with the cost of athyratron.

The specific nature of the invention, as well as other objects, uses,and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawing, in which:

Figure 1 is a plan view of the voltage responsive switch of thisinvention,

Figure 2 is an exaggerated sectional view of the volt-' age responsiveswitch of this invention,

Figure 3 is a wiring diagram showing the voltage responsive switch ofthis invention connected in circuit with a detonator,

Figure 4 is a wiring diagram showing a pair of voltage responsiveswitches of this invention connected in circuit with adetonator,

Figure 5 is a wiring diagram showing the voltage responsive switch ofthis invention in circuit with a detonator and with time delay means.

In Figures 1 and 2 there is shown a voltage responsive switch whichcomprises a piece of substantially pure aluminum 11, about the size of adime, and on which there is formed an anodized film 12, formed in a sixpercent by weight chromic acid bath. On the exceedingly thin anodizedfilm 12 there is placed a thin layer of silver 13, deposited through ascreen as is customary in printed circuits, and after its having beendeposited, the assembly is baked to remove the solvent in the depositedmaterial. The silver deposit has a diameter of about a quarter of aninch. A wire 14 is soldered to the silver layer, and a Wire 15 isconnected to the aluminum base 11, at a spot 16, where a hole has beenpunched through the base to expose the metal of the base, and the wire15 makes contact with the exposed area by a rivet or by being crimped inthe hole.

The assembly is next coated with a final coating of a plastic so thatonly the wires are visible.

The capacitance of a switch of the above approximate dimensions is ofthe order of .002 microfarad. The capacitance depends upon the area ofthe electrodes opposed to each other, upon the nature of the dielectricbe- 2,909,122 Patented Oct. 20, 19.59

ice

tween them and the thickness of the dielectric, and in the present casethe'film is exceedingly thin. The capacitance can, of course, bemadesrnaller by reducing the area of the silver layer, but thedimensions given herein have been found "acceptable for thepresent'purpose.

The base plate 11 is usually stamped from thin strips of substantiallypure aluminum which are anodized by being placed in a six percent byweight of chromic acid bath, and which have current passed through themfor about twelve minutes. The strips are next washed carefully to removethe electrolyte, and they are then dried in an oven, and after beingdried the silver electrodes are placed on the anodized film. After thewires 14 and 15 have been secured to the switch assembly the assembly isdipped in an epoxy-stearamide mixture to give mechanical strength and toprovide moisture-vapor resistance. I i

In Figure 3 the voltage responsive switch 10 is shown in a circuit whichcomprises alow-impedance pulsesource 17, a bias battery '18, and a lowimpedance detonator 19, and with the elements connected in series. Theswitch 10 has a normal resistance of the order of 3000'megohms, and whenthe film is ruptured and the switch is closed by a pulse of voltage fromthe pulse source in addition to that of the bias battery the resistanceof the'switch drops to a fraction of an ohm, so that the bias battery isnow directly in circuit with the detonator and a current of severalamperes flows in thecircuitto activate. the detonator.

In one run of switches assembled for use to activate the detonator thebiasing voltage is of the order of ten volts and the added pulse voltageis of the order of three volts. It will be understood that thesevoltages. given are not by way of limitation, for in the making of theseswitches quite acceptable switches may require a higher voltage and ahigher pulse voltage, within the limits of manufacturing tolerances,when they are used to activate a detonator.

When the film 12 breaks down, and the switch becomes closed, the switchremains as a low resistance device so that the bias battery can sendample current to the detonator.

In Figure 4 there is shown two of the voltage responsive switches 20 and21 in series with a bias battery 22 and a detonator 23. Voltageequalizing means comprise a resistor 24 and a resistor 25 connected inparallel with the switches 20 and 21, and their midpoint connection isconnected to the midpoint connection between the switches, by a wire 26.A source of pulses of voltage is connected by wires 28 and 29 to theswitch 21. The resistors 24 and 25 usually have a resistance of theorder of ten megohms, but this value is not critical just so long as itis high, and in the order of megohms. The switches have each a normalresistance of thousands of megohms.

It will be noted that the pulse source looks into the resistance of theswitch 21 and its shunting resistance 25, and that the remainder of thecircuit has a high impedance because of the high resistance of theswitch 20 and its shunting resistor 24. We may take the resistance ofthe battery and of the detonator as being very low, and but for theinserted resistance of the switch 20 and the resistor 24, the batteryand the detonator would appear as substantially a short circuit acrossthe pulse source. The bias battery voltage is that calculated to be thesum of the biasing voltages of the two switches.

When a pulse of voltage is received from the pulse source 27, it looksinto the capacitance of the switch 21, and the capacitance expedites thearrival of the pulse. The capacitance of the switch is immediatelycharged, and the pulse breaks down the film between the silver area andthe base material of the switch. When the switch 21 breaks down then theWhole voltage of the battery 22 is The battery voltage impressed acrossthe switch 20 when the switch 21 breaksdown is so much higher than thenormal bias voltage necessary for switch 20, it is not essential thatthe switches 20 and 21 have equal characteristics, and thischaracteristic of the circuit facilitates the use of switches that havenot been made to very close tolerances.

In Figure there is shown a circuit in which there is a time delaybetween the instant of closing a switch 30 and theactivating of adetonator 31 through a voltage responsive switch 32. A battery 33 isconnected through the switch 30, or other circuit closing device, andthrough wires 34 and 35 through a resistor 36 and a capacitor 37 so thatthe capacitor becomes charged when the switch to avalue at which itsvoltage is equal to the breakdown voltage of the voltage responsiveswitch 32, the switch breaks down, and the charge on the capacitordischarges through the detonator 31 to activate the detonator.

The time delay introduced by the resistor 36 and the capacitor 37 may bereadily calculated for any desired circumstance, and, of course, theenergy content of the capacitor can be made readily adequate to fire thedetonator,

It will be apparent that the embodiments shown are only exemplary and,that various modifications can be made in construction andarrangementwithin the scope of the invention as defined in the appended claim.

is closed. When the charge on the capacitor has risen We claim:

A time delay detonator activating circuit for ordnance fuzes comprisingin combination: a battery, a circuit closing device, a resistor, and acapacitor in series circuit relation, said battery charging saidcapacitor through said resistor when said device is closed, and theseries combination of a voltage responsive switch and a low-impedancedetonator connected in parallel across said capacitor, said switchcomprising a base of substantially pure aluminum having an exceedinglythin anodized film on one side thereon and having a thin layer of silverof a relatively smaller area secured to said anodized film, said.

layer of silver forming one electrode of said switch and thenon-anodized side of said base of aluminum forming the other electrodeof said switch, said switch substantially insulating said capacitor fromsaid detonator as long as the voltage on said capacitor is less than thepredetermined voltage required to break down said film of said switch,said battery having a voltage which is sufficient to charge saidcapacitor at least to said predetermined voltage, whereupon said filmwill break down causing the resistance across said switch to drop to avery low value, the capacitor thereupon discharging through saiddetonator causing activation thereof.

References Cited in the file of this patent UNITED STATES PATENTS

